The present invention relates to a structure for monitoring the characteristics of a fluid filled device, and, more particularly, to placing a diagnostic sensor within a fluid circulation flow path of the device and thereby obtain faster and more representative indication of an observable event.
To reduce the cost of maintaining, for example, a high or medium voltage electrical transformer, it is known to monitor certain operating characteristics of the transformer, whereby in the event an anomaly is detected, the transformer can be taken off-line (if necessary) and/or repaired as necessary. Properties that tend to indicate potential problems with a transformer and which may be monitored include the temperature of the tank in which the transformer is housed or the temperature of a coolant/insulating fluid, typically oil, disposed in the tank. Another monitored property is a gas concentration in the fluid or oil. Gases that provide diagnostic clues to a transformer""s state include hydrogen, methane, ethane, ethylene, carbon monoxide, carbon dioxide, acetylene, propane, and/or propylene. Other monitored transformer characteristics include moisture content, dielectric strength of the oil, and power factor values. When the measured or monitored value of any one or more of these properties exceeds predetermined levels, the transformer either likely is already operating in a fault mode, or will soon enter such a fault mode. Accordingly, such a transformer may be taken off-line (if necessary) and/or repaired. Generally, changes in monitorable properties that tend to indicate a transformer""s overall xe2x80x9chealthxe2x80x9d can be described as observable events.
Conventionally, sensors for monitoring the above-mentioned characteristics or properties of the fluid in a tank are mounted at existing external ports on the tank, such as drain valves or pressure relief means. Such an approach takes advantage of preexisting accesses to the tank of the transformer where fluid is easily accessible. Another known approach to sensing fluid properties is to locate a sensor at the top oil level in the tank via an internal mounting scheme. U.S. Pat. No. 3,680,359 to Lynch is an example of such an approach. Still another known approach is to provide a separate access hole or port in the tank and therefrom draw out an amount of fluid, or oil, considered sufficient to operate a sensor that is mounted external to the tank. Examples of this approach are disclosed in, for example, U.S. Pat. No. 4,058,373 to Kurz et al., U.S., Pat. No. 3,866,460 to Pearce, Jr., and U.S. Pat. No. 5,773,709 to Gibeault et al.
All of the approaches discussed above, however, position the sensor in a location that does not result in optimum detection by the sensor of the observable event. That is, conventional monitoring approaches are inaccurate to the extent that the monitoring is performed on fluid or oil that is drawn from a region adjacent to a tank wall or is near the top level of the fluid in the tank. Since the fluid in these regions tends to be more stagnant compared to fluid in other regions of the tank, the sample that is monitored might not accurately represent or indicate the manifestations of an observable event.
The preferred embodiment is directed to improving transformer diagnostic capability and reliability by selecting an appropriate sensor and locating that sensor, or a plurality thereof in the circulation flow path, i.e., the fluid circulation loop, of the electrical device. By positioning the sensor in such a way, an observable event can more effectively be witnessed and sensed by a sensor, thereby leading to more reliable, accurate, and timely measurements of observable events.
In the context of the present invention, the fluid circulation flow path is defined as a semi-closed loop where if an event occurs at a location in the loop, then all other sequential downstream locations will, in all likelihood, xe2x80x9cwitnessxe2x80x9d that event with some time delay.
In accordance with exemplary embodiments of the present invention, one or more sensors are positioned such that the fluid that is being sensed travels within the circulation flow path, whereby more accurate and efficient measurement of the properties and characteristics of that fluid can be obtained. In one embodiment, a sensor preferably is positioned in a radiator, or top or bottom radiator headers of the transformer. In another embodiment, a sensor preferably is disposed inside the transformer tank adjacent an inlet to or outlet from the radiator headers.
In a third embodiment, one or more sensors are positioned within the transformer windings. In this instance, the sensor preferably is wound together with the windings during manufacturing.
In a fourth embodiment, a sensor preferably is mounted on an end of a probe whose other end is disposed with the windings of the transformer. Such an approach reduces the sensor""s susceptibility to electromagnetic interference.
In a fifth embodiment, a sensor is positioned adjacent to the inlets or outlets of the flow channels of the windings.
In a sixth embodiment, multiple sensors are positioned within the circulation flow path and an observable event is monitored by some or all of these sensors whereby a time analysis of the observable event is effected.
In all cases, the sensor preferably is positioned within the circulation flow path of the fluid circulating in the transformer. As a result, all measurements undertaken by the sensor are more reliable, efficient, and accurate.